1. Field of the Invention
The present invention relates to a frame structure, and in particular to a transmitting/receiving apparatus and method using the frame structure.
2. Background of the Related Art
Generally, in order to achieve an effective data transmission when performing a long-distance data transmission in a wire public communication network, subscriber lines are first digitally multiplexed to determine a local circuit, and then a plurality of local circuits are multiplexed to determine a long-distance circuit. The digital hierarchies are defined by the transmission speeds of the respective stages of the multiplexing, and are in an integer multiple relationship with one another for facilitating the multiplexing. At present, the digital hierarchy is classified into three types, i.e., the U.S. and Canadian hierarchy, the European hierarchy, and the Japanese hierarchy.
As shown in FIG. 1, the U.S. and Canadian digital hierarchy includes DS1, DS2 and DS3 levels. DS1 is a digital hierarchy level having a transmission speed of 1.544 Mbps (megabytes per second), and is called T1. The DS1 includes 193-bit unit frames, and provides 24 channels.
DS2 is a digital hierarchy level wherein four DS1 unit frames are multiplexed. Here, DS2 is not considered part of the digital hierarchy itself, but is only used, as an intermediate hierarchy level, to create DS3 by multiplexing the DS2 unit frames. DS3 is a digital hierarchy level having a transmission speed of 44.736 Mbps, and a unit frame including 680 bits. The DS3 is used for transmitting a digital audio signal and a digital data signal.
As shown in FIG. 1, other digital hierarchy levels following DS3 may be created, for example, by using a frame structure wherein six DS3 unit frames are multiplexed and which has a transmission speed of 274.176 Mbps, or by multiplexing data to be transmitted using a synchronous transport module (STM-0) of the world standard synchronous digital hierarchy (SDH). In addition, other digital hierarchies preceding DS3 may be created. For example, the European hierarchy includes DS1E, which is a digital hierarchy level having a transmission speed of 2.048 Mbps, and is called E1.DS1E includes 256-bit unit frames, and provides 30 channels.
FIG. 2 illustrates a related DS3 frame structure. The DS3 frame of the related digital hierarchy has seven 680-bit unit frames which constitute a multiframe or a superframe having 4,760 (i.e., 680xc3x977) bits. Within the multiframe, 56 bits are used as a frame field, and the remaining 4,704 bits are used as an information field. The DS3 frame is created by multiplexing seven DS2 unit frames, and frame bits are added thereto for enabling the control of transmitted data. Accordingly, the DS3 frame has seven DS2 unit frames and the frame bits added thereto. The number of bits occupied by one DS2 frame with respect to the total number of bits of the DS3 frame is 671.609. (i.e. 4760 bitsxc3x976.312 Mbps/44.736 Mbps)
However, in order to make the number of bits occupied by one DS2 frame an integer number, 672 bits are allocated to the DS2 frame, and thus the number of bits occupied by the whole DS3 frame becomes 4,704 (672xc3x977) bits. At this time, since 672 bits instead of 671.609 bits are allocated to a DS2 frame, there is a difference of one bit between them. This one bit may belong to the information field, which serves as a justification bit (J1-J7), as shown in FIG. 2.
Recently, wire communication networks have been replaced with radio communication networks, which use the existing wire networks linked to radio networks. Under such a radio communication environment, a transmission error may easily occur due to an external noise that occurs when transmitting video data carried by a radio frequency using the DS3 frame structure shown in FIG. 2. The transmission error occurs because the existing DS3 frame structure only considers the data transmission based on the wire communication network.
However, the next-generation mobile radio communication system (IMT-2000) is required to provide multimedia services such as image signals, text signals, video signals, etc., as well as audio signals under the radio communication environment. Accordingly, a technique is required for radio-transmitting video signals broadcasted from broadcasting stations to television receivers or mobile terminals, by multiplexing the video signals. However, it is difficult for the DS3 frame structure, as shown in FIG. 2, to support the technique because the transmission speed becomes relatively slow when transmitting a digital television signal having a speed of 19.39 Mbps using the DS2 frame, while the waste in transmission speed becomes relatively large when transmitting the digital television signal using the DS3 frame.
Accordingly, a new digital hierarchy is required to transmit the digital television signal to the television receivers or mobile terminals through the radio communication network. However, this new digital hierarchy runs counter to the existing digital hierarchy based on the related art DS3 frame structure, and the related transmission speeds of the wire communication networks and the radio communication networks. Therefore, it is difficult to use both the new and existing digital hierarchies together.
An object of the present invention is to at least substantially obviate one or more of the problems due to limitations and disadvantages of the related art and provide at least the advantages set forth below.
Another object of the present invention is to provide an improved DS3 frame structure.
Another object of the present invention is to minimize transmission error during a video data transmission.
Another object of the present invention is to provide a video data transmitting/receiving method.
Another object of the present invention is to multiplex and transmit two video signals using the DS3 frame.
Another object of the present invention is to provide a video interface card.
Objects of the present invention can be achieved, in a whole or in parts, by a DS3 frame structure of a digital hierarchy including a plurality of unit frames, each unit frame having a frame field for controlling data transmission, an information field of signal data, and a channel coding overhead field having correcting data for correcting an error for the data.
Objects of the present invention can also be achieved, in a whole or in parts, by a video signal transmitting apparatus including a television signal line interface for converting at least two input video signals into TTL (transistor-transistor-logic) signals, a DS3 framer for multiplexing the converted video signals outputted from the television signal line interface and framing the multiplexed video signals into a DS3 frame structure, an encoder for inserting channel coding overhead bits into the DS3 frame outputted from the DS3 framer, and a line coder for coding an output of the encoder and transmitting a coded signal.
Objects of the present invention can also be achieved, in a whole or in parts, by a video signal transmitting method including the steps of converting at least two input video signals into TTL (transistor-transistor-logic) signals with a video signal line interface, multiplexing the converted video signals and framing the multiplexed video signals into a DS3 frame structure with a DS3 framer, inserting channel coding overhead bits into the DS3 frame with an encoder, and coding the DS3 frame having the channel coding overhead bits inserted therein and transmitting the coded DS3 frame with a line coder.
Objects of the present invention can also be achieved, in a whole or in parts, by a video signal receiving method including the steps of receiving video signals multiplexed to a DS3 frame and converting the video signals into TTL (transistor-transistor-logic) signals with a line interface, extracting original video signals from the DS3 frame with a DS3 deframer, compensating for or correcting a transmission error included in the DS3 frame with a decoder, and line-coding the compensated or corrected video signals to transmit the compensated or corrected video signals with a phase encoder.
Objects of the present invention can also be achieved, in a whole or in parts, by a video interface card using the DS3 frame structure of a digital hierarchy having a frame field, an information field, and a channel coding overhead field.
According to the above aspects of the present invention, two video signals can be multiplexed, and transmitted on a radio frequency with the basic structure of the related digital hierarchy, and the transmission error can be greatly reduced during the video data transmission.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.